Advertiser is charged for each ad/ CTA/ link that is being clicked on. This applies mainly to SEM and Display advertising.
Retargeting providers who are paid on clicks are incentivized to only look for clickers who have left an advertisers’ website.
As a result, frequency caps tend to be loose as the provider is chasing as many clicks as possible, and will serve adverts to a wider audience – and not always the users who are likely to be interested in the products being shown and that is most likely to convert